Q: I have a 1995 Ford E250 V8 van with 100,000 miles on it. Last September I went to the store for 15 minutes, when I came out the van wouldn't start. I thought it was the fuel pump so I tapped on the bottom of the tank but it didn't start. But after waiting five minutes it started right up. This happened again in April. I had a fellow crank the engine while I pounded on the fuel tank with a rubber mallet. I also tried pumping the gas pedal twice. It almost wanted to start, but not quite. Fifteen minutes later it started right up. Can there be any problem other than the fuel pump?

A: Here are the basics for DIY "crank but no start" troubleshooting — check for spark and check for fuel. During the period the van won't start, pull off one spark plug wire at the plug. Stick an old spark plug or a long screwdriver into the boot making sure it contacts the snap-on connector in the wire. Ground the plug body or hold the screwdriver shank about a quarter-inch from an engine bolt — using insulated pliers for the plug or the plastic/wood handle of the screwdriver so you don't ground yourself. Have someone crank the engine for a few seconds while you watch for a spark. If there's a strong spark, the problem is in the fuel system. If no spark, the ignition module may be overheating and shutting down.

The first DIY fuel system test is to determine if fuel pressure is available to the injectors. Try turning the ignition key on for two seconds, then off, a half-dozen times before trying to start the engine. This will run the fuel pump for two seconds each time, which may rebuild fuel pressure at the injectors. Now, crank the engine. If it starts, the fuel pump is fine but fuel pressure is bleeding down quickly after you shut the engine off. Possible causes are a leaky fuel pressure regulator on the fuel rail or the check valve mounted on the in-tank fuel pump.

Also possible: a simple case of vapor lock, where the fuel has boiled or percolated in the fuel rail near the engine upon shutdown. The DIY test/fix for this is to pour or squirt enough water over the fuel rail to cool it down, then try cranking the engine.

Q: I purchased a 2016 Hyundai Elantra and would like to switch to a full synthetic motor oil with 15,000 miles of guaranteed protection. What is the standard mileage interval between oil changes for synthetic oil?

A: The same as petroleum oil. Hyundai specifies API service rating "SM" or above in 5W-20 or 5W-30 weight and recommends oil changes every 7,500 miles in "standard" service or 3,750 miles in "severe" service conditions.

Neither Hyundai nor I recommend longer oil change intervals regardless of whether the lubricant is full synthetic or not. Both type of lubricants would be subjected to the same levels of contamination with water, gasoline and combustion byproducts and the additive package would be consumed at the same rate.

You could extend oil changes out to 15,000-mile intervals but the cost of oil changes is such a small percentage of the overall costs of ownership — fuel, depreciation, insurance, licensing and maintenance — that I see no economic or durability benefits in doing so.

Q: I have a 2008 Honda Civic whose passenger side map light quit working. I took the assembly apart and it needs a new switch. Dorman offers a similar switch but not the specific map light switch for this car. Where might I find one other than an auto salvage?

A: A Honda dealership, of course. Or an OE Honda part online. Prices seem to range between $35 and $40 depending on whether the vehicle has a moon roof. You could try the $12 pair of Dorman switches, but I'd go for the entire switch assembly for $35 at the dealership.

– Paul Brand. 'New engines are cheaper than new wives' – Ray Magliozzi (Car Talk), answering an unrelated question.

"So, the moral of the story is: Be sure to change oil on schedule, but never tell your wife to make sure it gets done!"

Paul Brand is the author of "How to Repair Your Car" and "How to Repair Your Truck and SUV," published by Motorbooks.